bcm74110-rng.c

  1// SPDX-License-Identifier: GPL-2.0
  2/*
  3 * Copyright (c) 2024 Broadcom
  4 */
  5
  6#define pr_fmt(fmt)	KBUILD_MODNAME ": " fmt
  7
  8#include <linux/module.h>
  9#include <linux/mod_devicetable.h>
 10#include <linux/kernel.h>
 11#include <linux/io.h>
 12#include <linux/delay.h>
 13#include <linux/platform_device.h>
 14#include <linux/random.h>
 15#include <linux/hw_random.h>
 16
 17#define HOST_REV_ID		0x00
 18#define HOST_FIFO_DEPTH		0x04
 19#define HOST_FIFO_COUNT		0x08
 20#define HOST_FIFO_THRESHOLD	0x0c
 21#define HOST_FIFO_DATA		0x10
 22
 23#define HOST_FIFO_COUNT_MASK		0xffff
 24
 25/* Delay range in microseconds */
 26#define FIFO_DELAY_MIN_US		3
 27#define FIFO_DELAY_MAX_US		7
 28#define FIFO_DELAY_MAX_COUNT		10
 29
 30struct bcm74110_priv {
 31	void __iomem *base;
 32};
 33
 34static inline int bcm74110_rng_fifo_count(void __iomem *mem)
 35{
 36	return readl_relaxed(mem) & HOST_FIFO_COUNT_MASK;
 37}
 38
 39static int bcm74110_rng_read(struct hwrng *rng, void *buf, size_t max,
 40			bool wait)
 41{
 42	struct bcm74110_priv *priv = (struct bcm74110_priv *)rng->priv;
 43	void __iomem *fc_addr = priv->base + HOST_FIFO_COUNT;
 44	void __iomem *fd_addr = priv->base + HOST_FIFO_DATA;
 45	unsigned underrun_count = 0;
 46	u32 max_words = max / sizeof(u32);
 47	u32 num_words;
 48	unsigned i;
 49
 50	/*
 51	 * We need to check how many words are available in the RNG FIFO. If
 52	 * there aren't any, we need to wait for some to become available.
 53	 */
 54	while ((num_words = bcm74110_rng_fifo_count(fc_addr)) == 0) {
 55		if (!wait)
 56			return 0;
 57		/*
 58		 * As a precaution, limit how long we wait. If the FIFO doesn't
 59		 * refill within the allotted time, return 0 (=no data) to the
 60		 * caller.
 61		 */
 62		if (likely(underrun_count < FIFO_DELAY_MAX_COUNT))
 63			usleep_range(FIFO_DELAY_MIN_US, FIFO_DELAY_MAX_US);
 64		else
 65			return 0;
 66		underrun_count++;
 67	}
 68	if (num_words > max_words)
 69		num_words = max_words;
 70
 71	/* Bail early if we run out of random numbers unexpectedly */
 72	for (i = 0; i < num_words && bcm74110_rng_fifo_count(fc_addr) > 0; i++)
 73		((u32 *)buf)[i] = readl_relaxed(fd_addr);
 74
 75	return i * sizeof(u32);
 76}
 77
 78static struct hwrng bcm74110_hwrng = {
 79	.read = bcm74110_rng_read,
 80};
 81
 82static int bcm74110_rng_probe(struct platform_device *pdev)
 83{
 84	struct device *dev = &pdev->dev;
 85	struct bcm74110_priv *priv;
 86	int rc;
 87
 88	priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
 89	if (!priv)
 90		return -ENOMEM;
 91
 92	bcm74110_hwrng.name = pdev->name;
 93	bcm74110_hwrng.priv = (unsigned long)priv;
 94
 95	priv->base = devm_platform_ioremap_resource(pdev, 0);
 96	if (IS_ERR(priv->base))
 97		return PTR_ERR(priv->base);
 98
 99	rc = devm_hwrng_register(dev, &bcm74110_hwrng);
100	if (rc)
101		dev_err(dev, "hwrng registration failed (%d)\n", rc);
102	else
103		dev_info(dev, "hwrng registered\n");
104
105	return rc;
106}
107
108static const struct of_device_id bcm74110_rng_match[] = {
109	{ .compatible	= "brcm,bcm74110-rng", },
110	{},
111};
112MODULE_DEVICE_TABLE(of, bcm74110_rng_match);
113
114static struct platform_driver bcm74110_rng_driver = {
115	.driver = {
116		.name = KBUILD_MODNAME,
117		.of_match_table = bcm74110_rng_match,
118	},
119	.probe	= bcm74110_rng_probe,
120};
121module_platform_driver(bcm74110_rng_driver);
122
123MODULE_AUTHOR("Markus Mayer <mmayer@broadcom.com>");
124MODULE_DESCRIPTION("BCM 74110 Random Number Generator (RNG) driver");
125MODULE_LICENSE("GPL v2");